Mini moth experiment

[BATTLEAXE]

Ok so here is the Mini Moth 2.0. It has been scaled up 150% and now has a bottom mounted vertical stabilizer. @BATTLEAXE the last picture shows how far back the CG moves when the wings sweep. More info coming soon.

These are some great pics, a lot of info can be gained from these. Your wing sweep doesn't look to drastic which explains the 1/2" change in CG. There are some things we can play with and a couple suggestions you have the option to consider. I think the one servo to swing both wings thing will work really well, it will be easy to program it to a "position 1/position 2" switch on your Tx. But once you scale up, like it was mentioned before you may have issues with wing flex at the pivot joint, especially under positive loading. Even in flight to switch from one mode to another may stress the pivot joint and the servo. If you look up KFM wing designs this might help out in the flex.

The rudder you installed isn't going to be very effective, although the fuselage will give you yaw stability to a degree it won't be enough to stabilize the plane, considering you have such a short distance from the wing to the tail. One way you can overcome this is to make your tail feathers a V-tail design. You already have them angled up some but in that position they just work like an elevator stuck in the nose up position. A V-tail will still give you the look your trying to achieve but be way more effective as control surfaces. And because of the short distance between your wing and tail they may work like elevons still. In a V-tail design you can eliminate the rudder all together, effectively cleaning up the design.

Something else you can play with as well is using small counter balance weights that pivot forward on an arm opposite of the wing, wing swings back, arm moves forward, maintaining your CG no matter where the wing sits. I don't know if this has been done before, just an idea off the top of my head. You may want to do some research on YouTube or google to see if there is anything on it. Again just an idea to try in the experimental design phase before you scale up. Actually a good question to you is, When you chuck glide with the wings back, does it pitch down compared to when the wing are forward?

 

[Cwildred.Gunn]

These are some great pics, a lot of info can be gained from these. Your wing sweep doesn't look to drastic which explains the 1/2" change in CG. There are some things we can play with and a couple suggestions you have the option to consider. I think the one servo to swing both wings thing will work really well, it will be easy to program it to a "position 1/position 2" switch on your Tx. But once you scale up, like it was mentioned before you may have issues with wing flex at the pivot joint, especially under positive loading. Even in flight to switch from one mode to another may stress the pivot joint and the servo. If you look up KFM wing designs this might help out in the flex.

The rudder you installed isn't going to be very effective, although the fuselage will give you yaw stability to a degree it won't be enough to stabilize the plane, considering you have such a short distance from the wing to the tail. One way you can overcome this is to make your tail feathers a V-tail design. You already have them angled up some but in that position they just work like an elevator stuck in the nose up position. A V-tail will still give you the look your trying to achieve but be way more effective as control surfaces. And because of the short distance between your wing and tail they may work like elevons still. In a V-tail design you can eliminate the rudder all together, effectively cleaning up the design.

Something else you can play with as well is using small counter balance weights that pivot forward on an arm opposite of the wing, wing swings back, arm moves forward, maintaining your CG no matter where the wing sits. I don't know if this has been done before, just an idea off the top of my head. You may want to do some research on YouTube or google to see if there is anything on it. Again just an idea to try in the experimental design phase before you scale up. Actually a good question to you is, When you chuck glide with the wings back, does it pitch down compared to when the wing are forward?

I really like the V tail idea i just need to research the optimal angle to set them at. The rudder was only minimally effective as you had predicted I had an idea to put under mounted winglets basically half way down the wings. I will begin to design the tail tonight I'm thinking something like a f117. When things are back it goes fast and straight like a dart. When the wings are forward I have to throw it softer and it floats away, if you throw too hard it goes up then down real fast.

 

[BATTLEAXE]

I really like the V tail idea i just need to research the optimal angle to set them at. The rudder was only minimally effective as you had predicted I had an idea to put under mounted winglets basically half way down the wings. I will begin to design the tail tonight I'm thinking something like a f117. When things are back it goes fast and straight like a dart. When the wings are forward I have to throw it softer and it floats away, if you throw too hard it goes up then down real fast.

The up and down fast is what's called a stall, the lift initially outweighs the forward momentum and pitches the plane up, losing speed and drops. If there was more height for it to drop it would gain enough speed to level out. Then again lose speed and drop. You will find this if a plane is under powered as well.

I can see this little project of yours has potential. Good luck and I will be following

 

[jfaleo1]

I really like the V tail idea i just need to research the optimal angle to set them at. The rudder was only minimally effective as you had predicted I had an idea to put under mounted winglets basically half way down the wings. I will begin to design the tail tonight I'm thinking something like a f117. When things are back it goes fast and straight like a dart. When the wings are forward I have to throw it softer and it floats away, if you throw too hard it goes up then down real fast.

Optimal v tail is 110 degrees. I like the idea of the v tail for this design. I really do not think the CG shift will be a big deal and I really like the shape. But you will have to trim with wing sweep. Set up the CG with wings forward, if it goes more nose heavy it is flyable, but tail heavy is bad. Currently it sounds like you are exactly opposite of this it is good when swept witch is making you tail heavy when sings are forward. Looks great though.

 

[L Edge]

As far as swept wings and CG go, i have a question. Where does the CG end up with the wings forward as compared to swept back, does the CG move back as well?

Yes, there was a difference with CG. I solved it a different way for the shift. After his build, will release it.

 

[L Edge]

Gunn, The tail feathers, rudder etc. is secondary for the moment. After you can, think about rudder, elevons etc. and it's location later. I am going to suggest even a different method for finding the CG that I use.

You need to design the rotational mechanism first. I see your movable wing ripping out with that setup or binding up. Also fluttering has to be address. I used standing up in a truck doing speed runs with the mechanism on to see if it works even before the stability problems.

Doesn' that make sense? If the wing doesn't swing, it's useless.

 

[Grifflyer]

Gunn do you have a 3D printer? If you did you could use a mechanism similar to this https://forum.flitetest.com/index.php?threads/ft-style-f-14-tomcat.58871/

 

[L Edge]

Just to show you what I am toying with is the talon.

http://pre03.deviantart.net/0574/th...rthrop_grumman_fa_37c_talon_by_bagera3005.png

Just think of what happens as the wing closes?

 

[BATTLEAXE]

Just to show you what I am toying with is the talon.

http://pre03.deviantart.net/0574/th...rthrop_grumman_fa_37c_talon_by_bagera3005.png

Just think of what happens as the wing closes?

Goes to a full delta and brings the CG forward. This is such a cool plane. Looks like something from a GI JOE cartoon lol

 

[L Edge]

Goes to a full delta and brings the CG forward. This is such a cool plane. Looks like something from a GI JOE cartoon lol

Doing 30 in a truck when wing is closing, fluttered it to death. Would be a unique plane if problems can be solved.

 

[BATTLEAXE]

Doing 30 in a truck when wing is closing, fluttered it to death. Would be a unique plane if problems can be solved.

I like the hang it out the window testing you do. Makes sense

 

[Vimana89]

Hello,
This is the start of a project that I want to scale up and get electronics on eventually. I call it the moth. I designed the airframe and wings based on a picture of a moth. It is intended to be a fantasy(fun) build and an exercise in aerocrafting. I have just started the hobby and this is my second project. If anyone out there has suggestions or questions or just good old fashioned comments on the build feel free to ask. (Edit I forgot to mention I want the wings to be able to sweep mid flight when I get the electronics sorted out. For now the wings are manually adjustable.)

Thanks
-Cwildred

Dude, that's awesome. I literally had the exact same idea to make a plane based on a moth wing. I was either going to go with a comet/moon moth or Atlas moth. I didn't plan to do variable wing sweep though, that's taking it to the next level. Can't wait to see this scaled up and motorized!

 

[Grifflyer]

Doing 30 in a truck when wing is closing, fluttered it to death. Would be a unique plane if problems can be solved.

I don't think that would happen, or be as bad if you were flying, because there is a ton of turbulence spiraling around your truck, there might be some turbulence when you are flying, but not as much as what a vehicle is causing.

 

[Cwildred.Gunn]

Okay so seems like I got some issues to sort out the CG is a big one which is linked to the other big one which is the sweep mechanism. I have looked a bit at what people are doing with the f14's and I like it but one thing I notice that will be different on the moth is the spacing between the wings. At the current scale I have about a 1/2" between the wings so if the wings are closed then I could have the servo arm running nose to tail in the 1/2" gap then the servo spins 90° to open the wings. However this wont help with the fluttering wings issue that L Edge has predicted. I dont want to move the pivot point because that will change the position of the wings either opened or closed depending on how I set it up initially. All of this considered I feel I should address problems as they arise. So based on what BATTLEAXE said to do with a v-tail I drew up a mod and cut it out. Did a few tests flights it definitely helped but it was not tracking perfectly straight(yaw) so I ended up adding some winglets(vert stabilizers) and then it was flying real straight. So without further delay, here are some pics.

 

[Cwildred.Gunn]

Just to show you what I am toying with is the talon.

http://pre03.deviantart.net/0574/th...rthrop_grumman_fa_37c_talon_by_bagera3005.png

Just think of what happens as the wing closes?

This thing is just too cool!

 

[Cwildred.Gunn]

Gunn do you have a 3D printer? If you did you could use a mechanism similar to this https://forum.flitetest.com/index.php?threads/ft-style-f-14-tomcat.58871/[/QUO

No 3d printer yet. Hopefully soon tho.

 

[Cwildred.Gunn]

Any thoughts on this slightly tweaked design? Also shows how the wing mechanism might work.

 

[Grifflyer]

That looks good, I don't see anything wrong with it.

 

[L Edge]

I don't think that would happen, or be as bad if you were flying, because there is a ton of turbulence spiraling around your truck, there might be some turbulence when you are flying, but not as much as what a vehicle is causing.

Aware of turbulance due to truck. In detail, use 2 x 4 extended out the side and length forward where I mount my testing item.(used it a number of times for other projects). By placing tufts, flow pattern can be analyzed at different speeds and what is happening to wing or whatelse.

 

[L Edge]

Any thoughts on this slightly tweaked design? Also shows how the wing mechanism might work.

View attachment 142510 View attachment 142511

You should have the joy of this design. Rather than tell you, why don't you list briefly what you would do in order to get this bird to fly.
I see it flying already.